Time-of-day announcing system



June 13, 1939. .1. BAUMFALK ET AL TIME-'OF-DAY ANNOUNCING' SYSTEM FiledAug. 6, 1936 ll Sheets-Sheet l P.L.WRIGHT @am ATTORNEY June 13, 1939. J.BAUMFALK ET Al.

TIME-OF-DAY ANNOUNCING SYSTEM Filed Aug. 6, 1936 1l Sheets-Sheet 2mAFF/C RE 6 IS TER TRAFFIC RE GIS TER TRA FF /C REGISTER /NvEA/TQRs: Fui

By AL. wma/lr A TTORNEV June 13, 1939. J. BAUMFALK Er AL Filed Aug. 6,1936 TIME--OF-DAY ANNOUNCNG SYSTEM 11 sheets-sheet 5 June 13, 1.939. .1.BAUMFALK ET A|.

TIME-OF-DY ANNOUNCING SYSTEMA Filed Aug. 6, 1956 June 13, 1939- J.BAUMFALK E- AL TIMEOF-DAY ANNOUNCING SYSTEM 11 sheets-sheet 5 Filed Aug.6, 1936 June y13, 1939.

J. BAUMFALK ETAL TIME-OF-DAY ANNOUNCING SYSTEM Filed Aug. 6, 1936/NVENTORSI 11 Sheets-Sheet 6 J. BAUMFALK BENNETT P.L. WRIGHT ATTORNEYJune 13, 1939. J. BAUMFALK ET Ax. 2,151,945

TIME-OF-DAY ANNOUNCING SYSTEM Filed Aug. 6, 1936 ll Sheets- Sheet 7 @LAP n/zro 726 J. BAUMFALK /lVl/ENTOIQSl W- BENNETT By RLJYRGHT June 13,1939 .1. BAUMFALK ET Al. 2,161,945

TIME-OF-DAY ANNOUNCING SYSTEM Filed Aug. e, 1936 11 sheets-sheet a J.BAUM/ALK /Nl/ENTORSI ENA/E77' By- RL. WRIGHT GPM ATTORNEY June 13,1939.v

J. BAUMFALK ET Al.' 2,161,945 .TIME-OFLDAY ANNOUNCING SYSVTEM FiledlAug.6, 1936 l1 Sheets-Sheet 9 A from/Ey June 13, 1939.l l J. BAuMr-ALK Er ALZ-,rllzsms .TIME-oF-DAY ANNOUNCING SYSTEM Filed Aug. e, 193e 11sheets-5h25# 1ov TIN/NG CIRCUIT 0F 57E.' BY STEP OFF/CE' J. /lvvnvronsv.

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`lune 13, 1939.

J. BAUMFALK ET AL TIME-OF-DAY ANNOUNCING SYSTEM Filed A115. 6, 1936 llSheets-Sheet l1 ATTORNEY Patented June 13, 1939 UNITED STATES PATENTOFFICE Bennett, Br

ooklyn, N. Y., and Paul L. Wright,

Short Hills, N. J., assignors to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationAugust 6. 1936, Serial No. 94,532

12 Claims.

This invention relates to telephone systems and more particularly tocircuits'for enabling subscribers to obtain pronouncements of the timeof day.

Heretofore provision has been made for enabling subscribers to obtainthe correct time of day by calling a central time service bureau.

The time service bureau is serviced -by an operator who in response toan incoming call observes the correct time as indicated by a time clockand informs the subscriber what the correct time will be when he hearsthe next tone signal.

Systems of this character have proven to be very satisfactory in largeexchange areas where 15 the volume of calls for the service warrants theconstant attendance of an operator at the central time bureau. In smalloiilce or exchange areas, however, more economical service may berendered by a time announcing machine of an automatic character sincethe volume of calls for time-of-day service would not justify the fulltime services of an operator. Furthermore, a demand has arisen forequipment which may be used by advertisers for supplying time-of-day 2service to subscribers together with pronouncements advertising theirparticular products.

It is therefore the object of the invention to provide trunking andcontrol facilities for enabling subscribers to obtain connections withan automatic time-of-day announcing machine whereby eiicient, dependabletime-of-day service may be furnished.

In accordance with the present invention central oice distributing,control, amplifier and transfer circuits are provided. All centraloflice trunks which are allocated for time-of-day service are connectedin multiple to the transfer circuit and may be manually or automaticallytransferred to either one of two duplicate channels or 40 trunksoutgoing to one or more time-of-day announcing machines. These machinesmay be 1ocated, if desired, at the central oiiice if the service is tobe supplied by the telephone company, or may be located at a subscriberspremises if such subscriber is furnishing time-of-day service as anadvertising medium. The central oflice trunks incoming to the centralolce may be of different types dependent upon whether the circuits areinstalled in manual, step-by-step or panel type exchange areas.

Each of the channels or trunks outgoing to the announcing machine isprovided with a one-way repeater equipment for enabling the transmissionof time-of-day pronouncements 'from the an- 55 nouncing machine to asmany subscribers Iin'es as may be simultaneously calling for such serv-5ice. rIhis trunk and repeater equipment is supplied in duplicate toavoid insofar as possible a disruption of the service. A distributingequipment is also provided for transmitting cutthrough signals andpronouncement termination signals to all incoming trunks which have beenseized by calling subscribers.

To obviate a disruption of service provision is made for automaticallytransferring calling trunks from one outgoing trunk to another outgoingtrunk under different conditions of failure. If after thev centralofilce equipment has been signaled from some incoming trunk thattime-ofday service is required, the announcing machine associatedtherewith has been started and a cutthrough signal has been transmittedto the calling trunk just prior to the beginning of the pronouncement,the repeater circuit of the channel or outgoing trunk then in servicedoes not receivev any speech current from the machine, a speech currentdetector in the repeater circuit functions to cause the automatictransfer of the incoming trunks to the second channel or out-f goingtrunk. Automatic transfer is also effected if a trouble condition isencountered on the outgoing trunk which is in service or if theannouncement machine does not start within a predetermined interval, orif upon transfer from one outgoing trunk to the other, voice current isnot detected in either repeater indicating possible trouble on bothtrunks or with the announcing machine at the time in service. In thelatter case, transfer back to the first trunk is effected and anautomatic transfer of both trunks to the other announcing machine ismade and if then no speech current is detected, a transfer is made tothe second outgoing trunk in a second attempt to iind a combination ofan outgoing trunk and announcing machine in operative condition.

It is believed that a better understanding of the invention will be hadby reference to the following description taken in connection with theaccompanying drawings of which:

Fig. 1 shows subscribers lines terminating in three types of offices andthe schematic representation of the call forwarding equipment of eachoflice, the oiiice represented in the upper portion of the figureillustrating switching equipment of the panel type, the oilicerepresented in the central portion of the figure being oi the manualtype and the office represented in the lower portion of the figureillustrating switching equipment of the step-by-step type; t

Fig. 2 shows three types of trunks accessible,

v manual oiiice 4and-trom the bank oi' a connector over the inner lowercontact of relay upper i's'pecuveiy, nein ,the bank of a nasi selector ma panel type oilice;trom thecalling Jack of a switch in a step-by-Btepoiilce:

Fig. 3 shows -atrunk accessiblefrom the bank of a selector of -astep-by-step oiiice;

Fig. 4 shows a transfer and distributing circuit to which trunks fromany one of the oillces shown in Figs. 2 and 3` may be multlpled;

Figs. 5 and B-taken together show the central oi'iice orv outgoing endoi' one channel or out going trunk;

Fig. 7 shows the distant end of two outgoing trunks or channels and theschematic representation of two announcing machines and an operatorsannouncing equipment;

Fig. 8 shows relay equipment for controlling the transmission ofcut-through and terminating signals to connected incoming trunks fandfor controlling the manual or automatic transfer of incoming trunks toeither o! the two channels or` outgoing trunks;

Figs. 9 and 1-0 taken together show the central oflice or outgoing endof a second channel or outgoing trunk;

Fig. 11 `shows a timing circuit for use when the system is installed ina manual area; and

Fig. 12 is a chart showing how the several figures of the drawing shouldbe arranged to disclose the complete circuits in accordance with theinvention. f

The announcingmachines 106 and 120 diagrammatically illustrated in Fig.7 may be of any desired type, the present invention not beingspecliically concerned with the machines per se, but rather with thetrunking circuits by which such machines may be associated with callingsubscribers lines. 'I'he transfer switches 100 Land 126 are provided forenabling two incoming channels or trunks to b e connected to eithermachine or to enable both trunks to be connected to one machine, but notenabling both machines to be connected to the same trunk.

Call from asubscriberv of a panel type olce It will rst be assumed thatthe subscriber whose line |00 terminates in the panel type oillcedisclosed in the upper portion of Fig. 1 initiates a call forascertaining the time of day and dials the directory number set asidefor such service. Upon the initiation of such a call thesubscrlbers linebecomes associated by means of line nder |0|, district ilnder |02 andsender selector |03 with the sender |04 and, when the subscriber dials,the line number becomes registered in the sender in the usual manner.The sender then proceeds to cause the setting of the district selector|05, oilice selector |06, incoming selector |01 and nal selector |00 toselect an idle trunk of the group allocated for time-of-day service.'for example, the trunk shown in the upper portion of Fig. 2.

Upon the seizure of this trunk a circuit is established from groundlover contacts of a sequence switch cam in the iinal selector |00,sleeve brush of selector |00 and the sleeve terminal of the selectedtrunk to battery through the windings of sleeve relay 200. Relay 200operates and establishes an obvious circuit for relay which alsooperates. Relay 20| upon operating establishes the circuit .of a tramcregister, if required,

from ground over its lower contact and the lower back contact of relay209, connects ground to conductor 203 and to the locking contacts ofrelays 206 and 200 over its upper front contact,

and over its inner lower contact establishes a start circuit. v

The start circuit may be traced from ground back contact of relay 200,conductor |0, lower back contact ofrelay 000, conductor 00|, lower backcontacts of transfer relay 400, conductor `40|, winding of start relay000 to battery. Re-

lay 000 operates and establishes a circuit over the upper lchannel oroutgoing trunk 0|0 which may be traced from ground, left winding ofrelay 60|,

ing "of repeating coil 102, in series through the f two windings ofrelay 103 and through the two 4windings of polarized relay 104, lowerleft winding of repeating coil 102, thence in parallel over thenext-to-inner back contacts of transfer relays 100 and,10|, ringconductor 606 of trunk 0|0, lower right winding of repeating coil 604,inner left iront contact of relay 600, left winding of relay 003, leftnormal contacts of relay 602, right winding of relay 00| to battery.Relay 103 now operates, but since the current flowing over this circuitpasses through both windings of differential relay 003 and is ofinsuillclent strength because of the inclusion oi' all the windings ofrelays 103 and 104, diilerential relay 603 and marginal relay 00| do notoperate at this time.

Polarized relay104- also does not operate since 106 which controls cam101,'if it is not already in operation, is established, which circuitmay be traced in part from ground at the contacts of relay 103, contactsof switch 106 and switch 150 to start conductor 100. The machine 105 isarranged to give a short closure of the contacts controlled by cam 101at an interval before it is ready to make the next time pronouncement,

. but the actual pronouncement will be delayed until a prnouncementsignal is received from the central o ce as hereinafter described. TheVclosure oi' the contacts by cam 101 shunts the upper winding of relay103 and the lower winding of relay 104 Vover a circuit which may betraced from the mid-point between the windings of relay 103, contacts ofswitch 106, contacts of switch 160,- cam contacts 100, contacts ofswitches 150 and 106 to the mid-point between the windings of relay 104.If machine 105 is also at thetime associated with the other trunk |0|0extending from the central oillce through the operation of transferswitch 120 to its upper position, a simila.r circuit is also establishedover the' cam contacts 1|0 and contacts of switch 150 around the upperwinding of relay 123 and the lower winding of relay 124, but withouteiIect at this time.

With one winding of each ofthe relays 103 and 104 shunted the strengthof current flowing over the trunk 6|0 is increased to such an extentthat marginal relay now momentarily operates and establishes an obviouscircuit forslowto-operate relay 030 and a circuit for relay 601 theupper contact of relay 20| which extends from battery through the` leftwinding of relay S01, back contact oi' relay S08, normal contacts oi'Arelay 635. contacts oi' relay 60|, conductor S08,` upper back contact'ofrelay 802 to ground at the upper normal contacts oi' relay 85|. When`relay 635 operates it opens the operating circuit of relay S01 but inthe meantime relay 601 has operated and closed a locking circuit foritself over its right winding and inner right iront contact and theright normal contacts of relay SII to ground on conductor 609. Relay 601also closes a locking circuit i'or start relay 600 extending through thewinding and inner right front contacts of relay S to ground at the innerleft i'ront contact of relay 601 and establishes the circuit of relaySI2 which may be traced from battery through the winding of relay SI2 toground at the outer left front contact oi' relay 601. Relay SI2 uponoperating, shunts 4the left windings of repeating coil S04 to preventacoustic disturbances due to signaling from reaching calling subscriberslines and to prevent the premature operation of the voice alarm relay500 on surges due to signaling.

Relay 601. at its middle right front contact also closes the circuit ofslow-to-release relay S36 which in turn closes the circuit of thedistributing relays 402, 403, etc., which are common to all incomingtrunks. This circuit may be traced from battery through the windings ofthese relays, lower back contact of transfer relay 404, conductor 405,upper back contact of relay 854, lower back contact of relay 805,conductor 808, right back contact of relay 6|5, left back contact ofrelay SI6, outer right back contact of relay 6|1 to ground at thecontact of relay 636. Relays 402, 403, etc., operate closing obviouscircuits for secondary distributing relays such as 406, 401, 408, 409,etc. Each relay such as 406 controls the establishment of cut-throughsignaling circuits for five incoming trunks and therefore as many commondistributing relays such as 402, 403 and secondary relays such as 406are provided as are necessary to close cutthrough signaling circuits forall of the trunks incoming to the central oilice.

It was assumed that a call for time-of-day service has caused theseizure of the incoming trunk disclosed in the upper portion of Fig. 2and that relay 20| thereof has been operated. With di'stributing relay406 now operated a circuit is completed for the cut-through relay 206 ofthis'I trunk which may be traced from battery through resistance 2| I,winding of relay 206, inner upper back contact of relay 209, conductor2| 2 upper contact of relay 406, conductor 203 to ground at' Relay 206now operates locking to ground over its inner upper front contact andthe upper contact of relay 20|, closing at its upper middle frontcontact one point in the operating circuit of relay 209, at its lowerfront contact bridging the upper back contact of relay 209 to insure thecontinuity of the start circuit over conductor 2|0 after relay 209operates and, at its upper and inner lower front contacts, connectingthe trunk conductors 204 and 205 to the conductors 2|4 and 2|5,respectively, and to the bridged retard coil 2| 3. With the coil 2I3 nowbridged across the trunk conductors 204 and 205 the incoming selector issignaled to advance to the talking position and to release the sender|04. If calls for time-of-day service are also present on other incomingtrunks vthey `will be cut through to the central oiiice trunks 2|4, 2|5in a similar manner through the operation of the secondary distributingrelays 40S, 401, etc.

Relay 601 upon operating also functions to start the timing relays SIIand S|4 to cause the measurement of a timing interval during which thecall charging equipment of the calling line or lines may become operatedbefore a time pronouncement is transmitted to such line or lines. RelayS I4 ls a diii'erentially wound relay the right winding of which isenergized upon the operation oi' relay 601 over a circuit extending fromground at the left normal contacts of relay SII, outer right contact ofrelay S01, back contact of relay 6|3 and back contact oi' relay S|4 inparallel, upper normal contacts of jack 6|8, right winding of relay SI4,resistance S38, lower normal contacts of jack 6|8 through resistance 620to battery. At the same time a circuit is closed from ground at the leftnormal contacts of relay 6| I, outer right contact of relay 601, backcontact of relay S|3 and back contact of relay 6I4 in parallel, lowernormalfcontacts of iack 6|9, resistance 631, left winding of relay 6| 4,upper normal contacts of vjack 6|9 through condenser 62| and resistance620 to battery over which circuit the condenser 62| is charged. So longas charging current iiows through the left winding or relay 6|4, relay6|4 will not operate since the windings thereof are energizeddifferentially. However, when condenser 62| becomes fully charged, thecharging current ceases to flow through the left winding of relay 6|4and relay 6|4 operates closing the circuit of relay 6I3 which may betraced from battery through its winding, the front contact of relay 6|4,thence as traced to ground at the left normal contacts of relay 6| Withrelays 6|4 and 6|3 both operated current now flows from ground at theleft normal contacts of relay 6|I, outer right contact of relay 601,right front contact of relay 6|3, lower normal contacts of jack 6I8,resistance 638, right winding of relay 6|4, upper normal contacts ofjack 6|8 through resistance 622 to battery and in a parallel path fromground as traced over the right front contact of relay 6|3 throughcondenser 62|, upper normal contacts of jack 6|9, left winding of relaySI4, resistance 631, lower normal contacts of jack 6|9 to batterythrough resistance 622. 'I'he current iiowing through both windings ofrelay 6|4 has now been reversed in direction through the operation ofrelay 6I3, but a similar diierential condition exists between thewindings of relay 6|4 which prevents this relay from immediately movingits armature to its back contact. However, when relay 6|4 does nallyoperate in the reverse direction it opens `the circuit of relay 6|3which thereupon releases.

In this manner relay 6|3 is intermittently operated, as long as relay601 remains operated, at a rate determined by the capacitance ofcondenser 62| and serves as a timed interrupter.

As above stated, the operation oi relay '601 caused the incoming trunkcircuit to cut through and the charging interval then starts. The firstoperation of relay 6|3 establishes the circuit of relay 6|1 whichextends from ground at therleit contact of relay 6| 3 through the inneky fight normal contacts and winding of relay 6 |11 resistance 623 tobattery and in parallel therewith through the winding of relay SIS andresistance 624 to battery. Relay 6|1 operates] andvlocks over its innerright alternate contacts to ground at the contacts of relay 636, butrelay 6|6 does.

not operate since its Winding is shunted by'a cli'- cuit extending fromground at the left contact ,75

4 of relay 6I6, the right back contact and winding of rela's 6I6, thenceover the inner right normal contac of relay 6I1 before relay 6I1operates to ground at the left contact of relay 6I3, or to ground overthe inner right alternate contacts of relay 6I1 after it operates toground at the contact-oi relay 606. Relay 6I1 upon operating opens thecircuit previously traced for relays 402, 403, etc. which now release inturn releasing relays 406, 401, etc. to open Athe cut-through conductorssuch as 2I2 of alLincoming trunks.

' Upon the first release of relay 6I3 the shunt around the winding ofrelay 6|6 is opened and relay 6I6 now operates in a circuit extendingfrom battery through resistance 624, winding of relay 6I6, inner rightalternate contacts of relay 6I1 to ground at the. contact of relay 636.When relay 6I6 again operates with relay 6I6 operated, ground isconnected from the left contact of relay 6I! over the inner right frontcontact of relayv 6I6 to a point between resistance 623 and the windingof relay 6I1 and relay 6I1 is thereby ,shunted down transferring thelocking circuit of relay 6l6 to the left front contact of relay 6I3 andestablishing a circuit for toperating relay 6I5 which may be traced frombattery through` the winding of relay 6I5, ,left front contact of relay6I6, left normal contacts of relay 6I1, to ground at the contact ofrelay 636. Relay 6I5 upon operating locks over its outer left frontcontact to ground at the contact of relay 636 and establishes thecircuit of distributing relays 4I0, 4II, etc. which are common to allincoming trunks. This circuit may be traced from battery through thewindings of these relays, the upper back contacts of transfer relayV400, conductor 4I2, middle left contact of relay 6I5 to ground at theouter right front contact of relay 6I6.

Relays 4I0, 4II,A etc. operate in turn causing the operation ofsecondary distributing relays 4I3, 4I4, 4I5, 4I6, etc. Each relay suchas 4I3 controls the establishment of cut off relay operating circuitsfor tive incoming trunks and therefore as many common distributingrelays such.

as 4I0, 4I I, etc. and secondary relays such as 4I3 are provided as arenecessary to close operating circuits for all of the trunks incoming tothe central oilice. Since thevtrunk shown in the upper portion of Fig. 2was assumed to be calling, the operation of relay 4I! closes a circuitfrom ground at its upper contact over conductor 2I6, middlel upper frontcontact of relay 206, inner lower normal contacts and winding of relay209` to battery. Relay 209 operates, locks over its inner loweralternate contacts to ground at the uppercontact of relay 20I, partiallyopens the start circuit over conductor 2I0 at its upper back contact andtransfers the cut-through conductor 2I2 from one terminal of thevwinding of relay 206 to the v other terminal of that winding. Similarcircuits are also established for other calling trunks through theoperationr of r'elays 4 I3, 4I4, etc.

' On the next release of relay 6I3 the locking circuit of relay 6I6 isopened and relay 6I6 releases, opening the circuits of relays 4|0, 4II,.etc. which release in turn releasing relays 4I3,

4I4, etc. which remove ground from the cut oi relay operating conductorsof all trunks. When relay 6I0 again operates, relay 6I1 operates overthe previously traced circuit and with relay 6I5 locked operated,establishes a circuit for relay 662 which-may be traced from batterythrough the winding of relay 602, right front contact of relay 6I6 toground at the left yfront contact of relu III.

" operating circuit for relay 6,05.

Relay 602 upon operating closes an obvious cfr- 8I5 extending frombattery through resistance 809. winding and upper normal contacts ofrelay 8I5, conductor 0I0 to ground at the outer left contact of relay602. Relay 'I6 .closes an obvious At its inner transferf'contacts relay602 reverses the direction 'of current flowing over the outgoing trunk6I0 through the windings of polarized relay 104 and; the windings ofrelay 106. Relay 6I6 operates and locks over its upperfalternatecontacts, the upper normal contacts of release key 6II to ground overthe -lower back contact of relay 060. Relay 600 upon operatingestablishes a holding circuit for relay 6I2 over its outer left contact,opens the. initial operating circuit of relay 601 at its back contact,at its inner left contact prepares an operating circuit for relay 625and at its right front contact establishes' anobvious circuit for relay6I I. Relay 6II is slow to operate to allow time for recording the'balyreversal at the station circuit of Fig. -7 and upon operating releasesrelay 601 which in turn causes the release of relays 636 and 6I5,suspends the operation of timing relays 6I3 and 6I4 and releases relays6I1, 602, 608 and 6I2 in cascade. Relayb600 upon releasing valsoreleases relay 6H.

During the time that relay 602 was operated to reverse the `directionofthe current owing over the trunk 6I0, polarized vrelay 104 operated toground conductor 1II at the announcing machine 105 to signal the'machine to proceed with the pronouncement.V When relay 602 releases,relay 104 -also releases to remove ground from conductor 1II whereuponthe pronouncement is given.. The announcing machine now impresses speechcurrent upon coil 1 I 2 which is now bridged through contacts'oftransfer switches 150 and 106 and through resistance's 1I3 and 1I4across the primary or right winding of repeating coil 102 and the shuntresistance 1I6. This speech current is thereupon inductively impressedthrough the secondaryior left winding of repeating coil 102,over backcontacts of transfer relays 100 and v10| and conductors 605 and 606 oftrunk 6I0,

upon the primary orfright'winding of repeating coil v604. With relay 6I2now released, the speech current is further impressed through the leit`mary winding of repeating coil 505, one secondary winding of which isconnected to the monitoring jack 506 and the other secondary windings ofwhich are connected in parallel over back contacts of transfer relay 4I1to the common incoming trunk conductors 2I4 and 2I5 which are connectedyover contacts of operated cut-through relays such as 206 and thence overthe incoming trunks such as 204, 205 tothe calling subscribers lines.The speech current in accordance with the correct time pronouncement istherefore amplied by the amplifying tube 506 and impressed upon eachcalling subscriber's line:

To prevent cross-talk between subscribers lines which may be at the sametime connected to the common trunk conductors 2I4, 2I5, should callingsubscribers attempt to talk over the established connection, eachincoming trunk such as 205, 204 is' provided with series resistances 2I1to 220, in-

clusive, which may be included or excluded by the patching connectionsindicated to give the best operation, and with series condensers 22| and222 interposed between the common trunk conductors 2|4, 2|5 and thecontacts of the cutthrough relay 206.

'Ihe amplifier tube 503 is a single stage amplifier the input circuit ofwhich is bridged by the potentiometer 501 for regulating the gain inaccordance with the output of the announcing machine and thecharacteristics of the outgoing trunk extending from the central officethereto to obtain the best results. Tube 508 is employed in connectionwith voice current alarm relay 500 `for detecting if speech ncurrent isbeing received from the announcing machine. The filaments of both tubesare lighted in a circuit extending from ground over the upper backcontact of transfer relay 404, conductor 4I8 through ballast lamp 509,which automatically regulates the amount of current owing through thefilaments, resistance 5| 0, filament of tube 508 in parallel withresistance 5| I, resistance 5|2, filament of tube 503 in parallel withresistances 5I3 and 5| 4 through resistances 5I5 and 5|6 and the normalcontacts of jack 5|1 to lament battery. Plate potential is supplied tothe plate of amplifier tube 503 through the primary windings ofrepeating coil 505, choke coils 5|0 and 5|9 and ballast lamp 520, andplate potential is supplied to the plate of voice current detector tube508 through the winding of voice alarm relay 500 and ballast lamp 520.

The voice alarm relay 500 is arranged to operate when voice currentsignals are received from the announcing machine, the grid of tube 508being biased by a circuit extendingthrough resistance 52|, the lowerwinding of transformer 522, resistance 523, the normal contacts of testkey 524, through resistances 5|3, 5|4, 5|5 and 5|6 and the contacts ofjack 5|1 to negative battery so that if no speech current is beingreceived through the upper winding of transformer 522, which is bridgedthrough condenser 525 across the output of amplifier tube 503, therewill be no current fiowing in the output circuit of tube 508 foroperating voice alarm relay 500. However, if speech current is beingreceived, the output current of tube 503 will be impressed upon theupper winding of transformer 522 thereby lowering the negative bias onthe grid of tube 508 to such an extent as to cause the operation ofrelay 500.

Key 526 is provided to enable a test to be made of the filament activityof the amplifier tube 503. With the key operated resistance 521 isshunted across the filament of the tube and if a filament transmissiontest set is then connected to test jack 528 and indicates a loss greaterthan one decibel, the tube is then known to be unsatisfactory. Thefilament activity test of the speech detector tube 508 is combined withthe test of the operation of the voice alarm relay 500. To make thistest the key 524 is operated and Without speech current present relay500 should operate. Failure to operate under this condition may indicateeither a defective tube or faulty adjustment of relay 500. The test jack5|1 is provided for measuring the filament current of the tubes, theresistance 520 and condenser 530 serving to protect the 'contacts of thejack. The input and output circuits of the amplifier tube may be testedthrough the test jacks 50| and 528 and monitoring on the amplifier maybe done over the monitoring jack 506.

Referring again to the operation of the announcing machine 105, when ithas finished the transmission of a, time-of-day pronouncement to thecalling line or lines and the cam 101 again closes the contacts`\109and`1| 0 short-circuiting 5 one winding of each of relays 103 and 104then, as previously described, marginal relay 80| again momentarilyoperates in turn causing the operation and locking of relay 801. If thepronouncement from the machine 105 has been properly re- 10 ceived andthe speech current detector tube 508 has operated voice current alarmrelay 500, relay 8|'5 will have been shunted down by a circuit extendingi'rom ground at the lower back contacts of relay 802, over conductor53|, contacts of relay 15 500, conductor 532 to a point betweenthewinding of relay 8|5 and resistance 808 and relay 805 will bereleased and therefore when relay 601 operates l as just described, acircuit will beV closed from ground over its inner left front contact,back 20 contacts of relays 6| 1, GIG and 6|5, conductor 808, lower backcontact of relay 805 and thence as traced to battery through thewindings of distributing 4relays 402, 403, etc. Relays 402, 403,

letc. will therefore operate in turn operating re- 25 lays 408, 401,etc. which prepare the cut-through conductors such as 2| 2 of allincoming trunks. For example, a circuit is established from ground overconductor 203, the upper contact of relay 400, conductor 2|2, the upperfront contact of 30 relay 209 thence through the winding and inner frontcontact of cut-through relay 206 to ground at the upper contact of relay206 thereby causing relay 205 to release and open the trunk circuit.-The calling subscriber is now unable to hear a 35 further timepronouncement. Similarly, all other calling subscribers Whose lines havebeen connected' to the announcing machine and who have received onecomplete time pronouncement are cut oi.

When the calling subscriber |00 hangs up his receiver the switchingequipment including selector switches |05, |06, |01 and |08 is releasedin the well-known manner, the release of final selector |08 releasingrelay 200 which in turn re- 45 leases relays 20| and 209.

Automatic transfer-Voice alarm failure It will now be assumed thatduring the" period that a time pronouncement should have been 50 sent,the speech current detector tube 508 detected no speech current andtherefore voice current alarm relay 500 failed to operate. Whentherefore relay 601 operated following the pronouncement period, relay805 will not have been 55 released and therefore the connection ofground to conductor 808 by the operation of relay 601 establishes acircuit over the lower front contact of relay 805, the upper backcontact of relay 800, conductor 429, normal contacts of relay 533, con'-oo ductor 420, winding of relay 804 to battery. Relay 804 operates,locking over the upper back contact of relay 800 and its own inner upperfront contact to ground at the middle upper back contact of relay 854,operating the transfer relay 4|9 65 over a circuit extending frombattery through the winding ofrelay 4|9, conductor 42| to ground at thelower front contact of relay 804, establishing an operating circuit forrelay 802 extending from battery through the Winding of relay 802, upperfront contact of relay 804 to ground at the upper front contact o frelay 805 and preparing to absorb the next cut-through impulse whichwill be given from the other outgoing trunk after the transfer theretohas been effected.

its outer front contacts closes obvious circuits for transfer relays 4|1and 423, relay 423 in turn closing obvious circuits for transfer relays400 and 404. With transfer relays 400, 404, 4|1 and 423 all operated acomplete transfer of the incoming trunks from the first outgoing trunkdisclosed in Figs. 5 and 6 to the second outgoing trunk disclosed inFigs. 9 and 10 is effected: .relay 4I1 transferring the trunkconductors2|4, 2|5 from the secondary windings of repeating coil 505 to thesecondary windings of repeating coil 905; relay 404 openingv thefilament-current supply circuit of tubes 503 and '508 thereby renderingthem ineffective and transferring the common distributing relays 402,403, etc. from their association with cut-through conductor 808,controlled by relay 601 of trunk 6|0 into association with cut-throughconductor 858 controlled by relay |001 of trunk |0I0;'relay 400transferring the common start conductor 2|0 from its connection overconductor 40| with the winding of start relay 600 of the first outgoingtrunk 6I0 into connection' over conductor 424 with the winding of startrelay |000 of the second outgoing trunk |0|0 `ancl transferring thecommon distributing relays 4|0, 4I I, etc. from their association withconductor 4|2 controlled by relay 6|6 of trunk 6|0 into association withconductor 425 controlled by relay I0|6 of trunk |0|0; and relay 423rendering effective the filament supply circuit of tubes 803 and 900 ofthe trunk circuit |0|0. .l

Relay 802 upon operating establishes over its lower front contact a newlocking circuit for relay 804, removes operating ground from conductors53| and 609, establishes a circuit for the trouble lamp 534 of theoutgoing trunk 6I0 which may be traced from battery through lamp 534,conductor 535 to ground at the upper transfer contacts of relay 802 andestablishes the circuit of alarm relay 843. This latter circuit may betraced from battery through the winding of relay 849, normal contacts ofkey 848, upper front contact of relay 802 to ground at the upper normalcontacts of relay 85|. Relay 848 establishes circuits to the oor alarmboard.

The removal of ground from conductor 608 releases relay 601 and allrelays controlled thereby and the transfenof the .common start conductor2|0 through the operation of transfer relay 400, from connection with'the winding of relay 600 releases relay 800 and relays 103, 104 and 60|if operated whereby the first outgoing trunk circuit is restored to itsnormal condition. With transfer relay 400 operated the start conductor2|0 is now extended over the lower back contact of relay 800, conductor80|, lower front contacts-- of relay 400, conductor 424 to batterythrough the winding of start relay |008. Relay |000 operates andestablishes acircuit over the trunk |0|0 which may be traced fromground, left winding of relay |00I, right normal contacts of relayl ingcoil 122, in series through the two windings of relay 123 and throughthe two windings of polarized relay 124, lower left winding of repeatingcoil 122 thence in parallel over the inner lower back contacts oftransfer relays 100 and 10|, ring conductor |006 of trunk I0 0, lowerright winding of repeating coil |004, inner left front contact of relay|000, left winding of relay |003, left normal contacts of relay |002,right winding of relay |`00| to battery. Relay 123 n'ow operates, butsince the current ows through both windings of differential relay |003and is not of the proper polarity or strength, relays IO0I, |003 and 124do not operate at this time.

Assume that the transfer switch 126 is operated to its lower position toassociate themachine 125 with the trunk |0|0 then when cam 121 of themachine 125 next closes its'contacts thereby shunting the lower windingof polarized relay 124 and the upper winding' of relay 123, marginalrelay |00| operates momentarily. Upon operating, relay IO0I establishesa circuit forrelay |001 which extends'from battery through the leftwinding of relay |001, back contact of relay |008, normal contacts ofrelay |035, contacts of relay I 00|, conductor 841, upper back contactof relay 852 to ground at the lower normal contacts of relay 85|. Relay|001 operates, locks over its right winding to ground on conductor 841under the control cf relay I0| I, establishes a locking circuit forstart relay |000, causes the operation of relay |0|2, causes theoperation of relay |036 and starts the functioningv of the timing relaysI0 I3 and |0I4 in the manner previously described in connection with theoperation of relay 601. Relay |036 is not effective to cause theoperation of the distributing relays 402, 403, etc. and relays u 406,401, etc. to transmit cut-through impulses to the incoming trunks sincethe circuit for operating relays 402, 403, etc. is at this time openA atthe inner lower back contact of operated relay 804.

Relays I0|1 and IOI6 are now operated and released sequentially underthe control of timing relay IOI3, relay |0|1 upon releasing with relay|0I6 operated causing the operation and locking of relay |0I5. Relay|0`I5 upon operating establishes the operating circuitfor thedistributing relays 4I0, 4| I, etc. over a circuit extending frombattery through the windings of these relays, upper front contacts oftransfer relay 400,

conductor 425, middle left front contact of relay |0|5 to ground at theouter right front contact vof relay |0I6. Relays 4|0, 4II, etc. operatein turn causing the operation of relays 4I3, 4|4, etc. but the latterrelays are ineffective at this time since at 'all incoming trunks whichhave previously been cut through by the operation ofv their cut-throughrelays 206 and whose cut-off relays 2 03 have been operated, theconductors such as 2I6 controlled by these distributing relays are openat the inner lower transfer contacts of relay 208 and at other incomingtrunks .which have subsequently been seized, but whose cut-throughrelays 206 have not yet been operated the conductors 2I6 are thereforeopen at the middle uppercontacts of relays 206. Upon the release ofrelay |0|6, relays 4|0, 4| I, etc. release in turn releasing relays 4|3,4|4', etc.

When relay |0I1 operates a second time under the control of timing relay|0|3, with relay |0I5 operated, the circuit of relay |002 is establishedrwhich maybe traced from battery, winding of relay |002, inner rightcontact of relay IOI5 to ground at the inner left contact of lrelayIOI1. Relay |002 upon operating closes an obvious circuit for relay |008over its outer right front contact, closes a circuit for relay 865extending from battery through resistance 853, winding andinner uppernormal contacts of relay 865, conductor 860 to ground at the outer leftcontact of relay |002 and at its inner transfer contacts reverses thedirection of current flowing over the outgoing trunk ||0 through thewindings of polarized relay 124 and relay 123. Relay 865 operates andlocks over its upper alternate contacts, the upper normal contacts ofrelease key 86| and the inner upper back contact of relay 850 to groundand closes an obvious circuit for relay 855. Relay |008 upon operatingestablishes a holding circuit for relay |0|2, opens the initialoperating circuit of relay |001, prepares an operating circuit for relay|025 and establishes an obvious operating circuit for relay |0| Relay|0|| operates after an interval and causes the release of relay |001which in turn causes the release of relays |036 and |0|5, suspends theoperation of timing relays |0|3 and |0|4 and releases relays |0|1, |002,|008 and 50| 2 in cascade, relay |008 upon releasing also releases relay|0| l.

Relay 855 upon operating, as just described, establishes an operatingcircuit for relay 803 which may be traced from battery, winding of relay803, upper back contact of yrelay B50, lower normal contacts of releasekey 86|, lower transfer contacts of relay 803, middle upper-frontcontact of relay 804 to ground at the inner lower front contact of relay855. Relay 803 upon operating locks in a circuit as previously tracedvto its transfer contacts and thereover to ground at the lower frontcontact of relay 802.

During the time that relay |002 was operated to reverse the direction ofcurrent flowing over trunk |0| 0, polarized relay 124 operated to groundconductor 13| of the announcing -niachine 125 to signal the machine toproceed with.

the pronouncement. When relay |002 releases, relay 124 also releases toremove the ground-from conductor 13| whereupon the pronouncement isgiven. The machine now impresses speech current on coil 132 which is nowconnected over the lowercontacts of transfer switch 126 with repeatingcoil 122. The secondary windings of repeating coil 122 are connectedover back contacts of transfer relays 100 and 10| to trunk |0|0 andthence with the primary windings of repeating coil |004. The secondarywindings of repeating coil |004 being linked through repeating coil 902tothe input of amplifier tube 903, the speech current is amplied therebyand impressed upon the repeating coil 905 and from thence over frontcontacts of operated transfer relay 4|1 upon all incoming trunks whichhave been associated with the central office through the operation oftheir cut-through relays 206. If the circuits are functioning properlythe calling subscriber whose line |00 has been associated over trunkv204, 205 with the central office should receive the time pronouncement.If speech current is received properly the speech current detector tube908 will now respond thereby operating speech alarm relay 900. Withrelay 900 operated, relay 865 is now shunted down over a circuitextending from ground at the lower back contact of relay 852, conductor93|, contacts of relay 900, conductor 932 to a point between the windingof relay 865 and resistancev 85.9 thereby releasing relay 855.

When the announcing machine 125 has iinished the transmission of thetime-of-day pronouncement and the cam 121 again closes its contacts,relay |00| is again momentarily operated in turn operating relays |001and |030.

Under the assumption that speech current has been properly received andthat relay 855 has been released, relay |036 now closes a circuit frombattery through the windings of distributing relays 402, 403, etc.,lower front contact of transfer rela-y 404, conductor 426, upper frontcontact of relay 803, lower back contact of relay 855, conductor 858,back contacts of relays |0|5, |0|6 and |0|1 to ground at the contact ofrelay |036. Relays 402, 403, etc. will now operate causing the operationof relays 406, 401, etc., to transmit cut-through signals to allincoming trunks over conductors such as 2|2. These signals are electiveto release the cut-through relays of all incoming trunks which havereceived,x the time pronouncement, or to cut through such trunks as arewaiting for the time pronouncement.

Should the speech current detector tube 908 of the trunk |0|0 fail todetect speech current and relay 900 not operate, then relay 855 would beoperated at the time relay |036 operated following the announcementperiod. In this case the connection of ground to conductor 858 by theoperation of relay |036 will complete a circuit over the lower frontcontact of relay 855, normal contacts of relay 933, inner upper backcontact of relay 800, winding of relay 854 to battery. Relay 854 uponoperating establishes a circuit .for relay 852 extending from batterythrough the winding of relay 852, lower front contact of relay 854 toground at the upper front contact of relay 855 and a circuit for relay853 extending from battery through the winding of relay 853, inner lowerback contact of relay 800, lower normal contacts of release key 8| lowertransfer contacts of relay 853, inner upper front contact of relay 854to ground at the inner lower front contact of relay 805. Relay 852 uponoperating establishes a locking circuit for relay 854 extending fromground over its lower front contact, inner lower front contact of relay854, normal contacts of relay 933, inner upper back contact. of relay800 to battery through the finding of relay 854, establishes a lockingcircuit for relay 853 extending from ground over its lower frontcontact, the transfer contacts of relay 853, lower normal contacts ofkey 8| inner lower back contact of relay 800 to battery through thewinding of relay 853, establishes a circuit from ground over its innerupper front contact and conductor 935 for lighting the trouble lamp 934associated with the trunk |0|0 and establishes a circuit over its upperfront contact for the alarm relay 849.

When the maintenance man in response to the lighting of trouble lamp 534and the operation of the floor board alarms, clears the trouble on therst trunk 6|0, he will operate release4 key 8|| thereby opening thelocking circuits of relays 8|5 and 853. Relay 8|5 upon releasing,releases 805 and 802 in turn releasing `relays 803 and 804 andextinguishes the trouble lamp 534. lWith relay 804 released and relay854 operated, the operating and locking circuits of transfer relay 4|9are opened and relay 4| 9 releases in turn releasing transfer relays400, 404, 4|1 and 423. .The incoming trunks are now transferred back tothe rst outgoing trunk 6|0. Similarly, if the trouble on the secondoutgoing trunk |0|0 is first cleared, the release key 86| is operatedthereby releasing relays 865 and 803, relay 865 upon releasing in turnreleasing relays .855 and 852 which in turn releases relays 853 and 851|and extinguishes the trouble lamp 934 When the trouble is cleared onboth trunks and both relays 802 and 852 have been released, re-

' lay 849 releases stilling the iloor board alarms.

The iioor board alarms may also be silenced by the maintenance manthrough the operation of key 848.

Automatic transfer- Line trouble condition L its lower front contact,the upper normal contacts of release key 8|| to ground at the lower backcontact of relay 850, establishes a circuit from ground over its innerupper front contact for relay 802 and a circuit over its upper frontcontact, the uppery back contact of relay 800, winding of relay 804 tobattery. With relays 802 and 804 operated, transfer relays 400, 404,4|1, 4|9 and 428 are operatedand the incoming trunks are thentransferred into connection with the second outgoing trunk in the mannerdescribed. Relay 802 upon operating also causes the trouble lamp 594associated with trunk 8| 0 to be lighted and the iloor board alarm relay849 to be operated.

If troub es occur on the second outgoing trunk' |0|0, relays |003, 851,852 and 854 operate in a similar manner and the trouble lamp 934associated with trunk) |0|0 is lighted. Afterthe trouble is found andeliminated the circuits are restored to their original condition by theoperation of either release key 8|| or 86| dependent on the trunk uponwhich the trouble has occurred.

Automatic transfer-Timed 'trouble condition vision is made for causingthe automatic transfer of incoming trunks to the other outgoing trunk|0|0.

When the start relay 600 operates, as soon as battery is connected fromthe common timing circuit, a circuit is completed over interruptercontacts |039, -conductor 621, winding of pick-up relay 629, backcontact of relay 630, right normal contacts of relay 625, conductor-83|, back contact of relay 801, conductor 32 to ground at the outerright front contact of relay 600. Relay -629 operates and locks tobattery over its inner left front contact. If the trunk circuit operatessatisfactorily, relay 602 will be operated from the announcement machine105 in turn operating relay 608 as previously described and relay 608will establish a circuit from ground over its inner left front contact,right winding of relay 625 to battery over the outer left front contactof relay 629. Relay 825 uponoperating locks in a circuit from batteryover the outer left contact of relay 629, left winding and inner leftfront contact of relay 625, conductor 633 normal contacts of monitoringjack 606, conductor 421 to ground at the back contacts ofdistributingrelays 406, 401, etc., and closes an obvious circuit for relay 630.Relay 630 operates and locks over its left contact to ground over theinner right contact of relay 629 and opens the locking circuit of relay829 but with relay 625 operated,

relay 829 is maintained operated in a circuit from battery over .itsinner left front contact and winding, right transfer contacts of relay625 thence as traced to ground at the outer right contact of start relay600.

, At the end of the transmission of the pronouncementsignal to theannouncing machine which occurs upon the release of relays 602 and 608and the subsequent operation of relay 636 thereby operating relays 4|3,4|4, etc., the operating and locking circuits of relay 625 will beopened and relay 625 will release and cause the release of relay 629which will be followed by the release of relay 630.

If, however,l trouble occurs and relays 625, 629 and 630 do not releasebefore ground becomes connected from the timing interrupter contacts-|040 a circuit is completed therefrom over conductor 628, the rightfront contact of 4relay 629,

'conductor 634, conductor 626 to battery through 804, the operation oftransfer relays 400, 404,.

4|1, 4|9 and -423 to transfer the incoming trunks to the second outgoingtrunk I0|0 and to light the trouble lamp 534. In a similar manner,relays |025, |029 and |030 function under the control of the commontiming circuit if the trouble conditions arise in connection with trunk|0|0 and the announcing machine 125.

Automatic switch-over at announcer machine If both outgoing trunks orannouncement channels fail to operate and cause the lighting of troublelamps 534 and 934 associated therewith in the manner previouslydescribed, the trouble may be due to faulty station equipment in onechannel and trunk or central oiiicetrouble in the other channel. For4this reason provision is made to send a signal to the `station to causethe interchange of the two trunks and associated announcing machine.Under this condition both relays 802 and 852 Will be operated and willclose a circuit for relay 846 extending from battery, winding of relay846, upper back contact of relay 845, inner lower front contact of relay852, inner lower front contact of relay 802 to ground. Relay 846 uponoperating locks over its lower front contact and the front contacts ofrelays 802 and 852 independent of relay 845 and closes an obviousoperating circuit for relay 85| and an operating circuit for relay 845.This latter circuit may be traced from ground over the upper frontcontact of relay 846, the transfer contacts and winding of relay 845 tobattery. Relay'85l upon operating removes ground from conductors 609 and841 over which relays 601 and |001 are operated and locked andestablishes an obvious operatingcircuit for slow-to-operate relay 850.Relay 845 upon operating locks over its transfer contacts under thecontrol of release key 844, closes the circuit of lamp 843, opens at itsupper back contact the initial operating circuit for relay 846, closesat its inner upper front contact a holding circuit for alarm relay 849and at its mididle upper front contact establishes a circuit from toallow sumcient time for relays 548 and 85| to become magneticallysaturated and then upon operating establishes an obvious circuit forrelay 800, disconnects ground from contacts of release keys 8|| and 86|and opens the circuit of relay 858 which now releases. The removal ofground from the contacts of keys 8I| and 86| now causes relays 8I5 and865 to release in turn releasing relays 885 and 855 and causing relays801 and 851 to release if they have been operated. The operation ofrelay 800 opens at its lowex` back contact the start conductor 2 I 0, atits inner lower back contact opens the circuit of relay 858, at itsinner upper back contact opens the circuit of relay 854 and at its upperback contact opens the circuit of relay 804. Relays 804, 858 and 854 nowrelease.

The above described operations cause the release of relays 802 and 852and all operated relays-of Figs. 6 and 10. Relays 802 and 852 uponreleasing open the locking circuit oi' relay 845 which 'releases in turnreleasing relays 85|, 850 and 800 to permit another trial of both trunksor channels to be made with the announcing machine 105 now connected totrunk '|.0I0 and machine 'I25vconnected to trunk 6| 0 through theoperation-of transfer relays |00 and 10|. Relays 846 and 85| are madeslow tov release to permit the other relays of the circuit sufficienttime to release as just described. 'I'he second trial of both channelsis now made in the manner previously described, but since relay 845 islocked operated under the control of' key 844, if a failure results onboth channels on the second trial,

the operation of relays 802 and 852 is ineffective to cause thereoperation of relay 846. Relay 845 remains operated until the troubleon both channels is cleared Iat which time the maintenance man willoperate key 844. No provision is made to prevent interference with acall when key 844 is operated so therefore it should be operated whenthere are no calls in progress.

Manual transfer If the maintenance man desires to transfer from onechannel to the other he may do so by operating either the key 8I2 or key862. To transfer from the first channel or trunk 6 I 0 to the secondchannel or trunk |0I0, key 8I2 will be operated thereby causing theoperation of relay 806. If there is no call in progress and thereforestart relay 600 is not operated, a circuit is established at once fromground 'over the outer left back contact of relay 600, conductor 8|8,lower front 'contact of relay 806, upper back contact of relay 800,winding of relay 804 to battery thereby resulting in the operation ofthe transfer relays 400, 404, 4I1, 4I9 and 428 and the immediatetransfer of the incoming trunk to the second channel or trunk IOI0 inthe manner previously described.

If, however, there is a call present and relay 600 is operated, relay806 is locked when it operates 'over its upper front contact andconductor 8| 4 to the outer left front contact of relay 600 and relay804 is not therefore voperated until conductor 8I8becom`es groundedthrough the operation of relays 6I5 and 6|6 which will not occur untilafter a pronouncement that may be in progress has been completed so thatthere will be no interference with such pronouncement.

Should the second channel or trunk |0I0 be in service and themaintenance man desire to transfer incoming trunks to the first channelor trunk 6 I 0, he may do so by operating transfer key the incomingtrunks from the nrst to the second channel.

Operating test of either channel An operating test of either channel maybe made by plugging a monitoring receiver into the monitoring jack ofthe channel to be tested. For example, should a test of the firstchannel of trunk 6I0 be desired, the maintenance man will plug intomonitoring Jack 506 whereby the monitoring receiver will be connected tothe first secondary winding of repeating coil 505 and a circuit will beestablished for relay 588 extending from battery throughl the winding ofthis relay, contacts of jack 505, conductor 586 to ground at the innerupper back contact of relay 802. Relay 588 upon operating will connectstarting ground over conductor 40| for operating start relayA 600 of thechannel, supply filament ground over its middle left contact for thetubes 508 and 508 of the channel, open the operating circuit of relay804 at its outer left contact and at its inner contacts preparescircuits for lamps 840 and 84|. Ii' the circuits of the first channelfunction correctly the cut-through signal transmitted forv operatingdistributing relays 402, 408, etc., as previously described, will nowlight lamp 84| over a circuit from ground applied to conductor 808 bythe operation of relay 686, lower back contact of relay 805, upper backcontact of relay 854, conductor 405, inner left front contact of relay588, conductor 581 through lamp 84| to battery indicating that thecut-through signal has been properly. received. Also, the signaltransmitted for operating distributing relays 4|0, 4|I, etc. will nowlight lamp 840 over a circuit extending from ground applied to conductor4I2 upon the operation of relays 6| 5 and 8I8, thence over the innerright contact of relay 588, conductor 588 to battery through lamp 840indicating that the signal has been properly transmitted and thepronouncement will then be heard in the monitoring receiver. When themonitoring receiver plug is removed from Jack 506, relay 588 willrelease thusfrestoring the circuits to normal.

Should the maintenance man monitor upon the second channel, relay 988will be similarly operated to close the filament circuit of the tubes908, and 908, to close the start circuit extending through the windingof relay |000 of the second channel, to open the operating circuit o1'relay 854 and to prepare the circuits of lamps 840 and.84|. When thecut-through signal is transmitted to relays 402, 408, etc. by thegrounding of conductor 858 as previously described, the circuit of lamp84| will be established from ground on conductor 858, thence over thelower back contact of relay 855, inner lower back contact of relay 804,inner left front contact of relay 983, conductor 581 to battery through'lamp 84|. When the signal is transmitted to relays 4|0, 4| I, etc. bythe grounding of conductor 425, the circuit of lamp 840 will beestablished over the inner right front contact of relay 988, conductor588 to battery through lamp 840. If these lamps light momentarily insuccession followed by the reception of a pronouncement in themonitoring receiver, the maintenance man will know that the channel isfunctioning properly.

